Lead acid batteries are commonly used in automobiles, recreation vehicles, aircraft, and so forth where a strong current of electricity is necessary for starting of an internal combustion engine. Lead acid batteries operate on the principal that when two dissimilar metals are immersed in an electrolyte, a voltage develops between them.
The dissimilar metals in conventional lead acid batteries are characterized as positive plates and negative plates. Positive plates are made from a compound of lead and oxygen forming lead dioxide (PbO.sub.2). The negative plates are made of lead metal typically spongy in texture. The electrolyte consists of sulfuric acid (H.sub.2 SO.sub.4) and water. Common battery electrolyte concentration is approximately 25% volume of acid and 75% water.
During the discharge of a battery, when current flows from the battery to an external load, lead in the positive plate leaches off and combines with sulphite from the electrolyte to form lead sulphite (PbSO.sub.4) on the positive plates. The negative lead electrode disassociates into free electrons and positive lead ions. Thus, the lead dioxide combines with the positive hydrogen ions in the electrolyte with the returning electrons to form water, thereby releasing lead ions into the electrolyte to form additional lead sulphite. As the oxygen on the positive plates combines with hydrogen from the sulfuric acid to form water, the result is a reduction in the concentration of the electrolyte thereby lowering the specific gravity of the electrolyte. A fully charged battery will have an electrolyte specific gravity of 1.265 when corrected to 26.7.degree. C. A battery electrolyte with a specific gravity of 1.120 is considered completely discharged.
When the battery is charged, a current is passed through the battery in the opposite direction to restore the active chemicals to their original condition. In this manner, the lead sulphite (PbSO.sub.4) that was formed on both plates is broken up into Pb and SO.sub.4. The water disassociates into hydrogen and oxygen. In this manner, the sulphite can now combine with the hydrogen to reform sulfuric acid (H.sub.2 SO.sub.4) while the oxygen combines with the lead to form lead dioxide (PbO.sub.2). The sulfuric acid that is forming is more dense than the water that is disappearing which results in the specific gravity of the electrolyte to increase.
Lead acid batteries may employ antimony as a constituent to increase the strength and other physical properties of lead. When antimony is added to the lead in both the positive and negative plates, it is referred to as an antimony-antimony battery, or deep cycle. However, antimony increases hydrogen production at the negative plate, and oxygen at the positive plate, as water is being decomposed. This can be visualized through bubbling, gassing, or misting. The result is a decomposed mixture which forms a highly explosive situation. This type of battery is used in recreation vehicles, electric cranes, electric cars, golf carts, and so forth.
An alternative to the deep cycle battery is the recently introduced calcium-antimony battery, also referred to as a hybrid battery. This battery has a positive cell consisting of antimony integrated into the lead and a negative cell consisting of calcium integrated into the lead. The hybrid battery maintains some of the beneficial properties of the deep cycle battery, such as repeatable cycling, while the hydrogen gas production is decreased. Thus, the need for adding water is reduced but not eliminated making it a low maintenance battery. The hybrid battery allows for general use with nearly any type of vehicle.
Still another style of battery is the calcium filled battery which is commonly referred to as the "maintenance free" battery. The positive and negative plate cells each contain calcium eliminating the need to add water during the life of the battery. The lack of antimony reduces gas generation and associated depletion of the electrolyte. A disadvantage of the maintenance free battery is the lack of mechanical properties comparable to the antimony battery, in particular, the ability to deep cycling such a battery is not possible. Deep cycling causes the calcium plate cells to grow mechanically or creep. Should creep become excessive, adjacent parts may short out thereby disabling the battery or severely reducing its capacity. This prohibits the use of a calcium-calcium battery for use in deep discharge applications wherein the breakdown of the grid-paste interface results in loss of battery capacity.
Both the antimony-antimony and calcium-antimony batteries, commonly referred to throughout this specification as lead acid antimony batteries, are capable of withstanding repeated cycling and will generally accept a charge more readily than a calcium battery. However, higher charge acceptance of the antimony battery causes increased water consumption, gassing, and the resultant external corrosion problems. If the lead antimony battery is not properly maintained, battery trays, and cables will require regular replacement due to corrosion and possible boil over problems. Water can be added to a battery but is a maintenance step seldom performed by the average consumer. Further, low mineral content water must be used and should the battery be overfilled, an overflow of the cells may occur causing metal degradation to the area surrounding the battery.
The sulfate conversion and hydrogen production also causes a strong offensive odor which can be harmful to breath for people with serious health problems. For example, wheelchair occupants must endure fumes if their battery operated wheelchair is recharged while occupied. Recreational vehicles and boats may have their batteries cycled repeatedly while parked wherein misting from the battery may cause corrosion of the surrounding metals. For this reason such vehicles may employ a specialty battery compartment designed to control the corrosion. Alternatively, the batteries may be placed within non-corroding boxes to prevent spreading of fumes. However, closed spaces may increase acid deposits promoting post and cable corrosion resulting in current leakage across the battery top.
In an effort to reduce the aforementioned problems associated with lead antimony batteries, prior art teachings disclose various electrolyte additives. One such additive is the use of oil as set forth in U.S. Pat. No. 1,512,485. In this disclosure, the use of an electrolyte containing a hydrocarbon is proposed such as "reduced oils" made from the residual of crude oils. While the disclosure describes the use of an oil, it fails to provide an operative electrolyte.
U.S. Pat. No. 4,427,750 discloses a specialized battery including an oil additive stating an electrolyte of 20% volume sulfuric acid and 80% refined mineral oil with acetic acid. This disclosure does not operate with conventional batteries as the proposed amount of mineral oil and acetic acid provides little or no battery capacity. The positive and negative plates cannot be immersed in oil or acetic acid without having a detrimental effect on the battery's capacity.
Thus, what is lacking in the art is an electrolyte additive that reduces or eliminates hydrogen gassing and associated water loss in lead antimony batteries in such a level so as to beneficially effect the capacity of the battery providing longevity through the acceptance of increased cycling amounts.